Cell Membrane & Transport SBI4U 2016/10/18
Cell membrane All cells exist in an aqueous environment, separated by their membrane; The membrane regulates which substances pass into or out of the cell; It is composed of a phospholipid bilayer, which contains cholesterols, carbohydrates and proteins; These proteins may be used for: Transport; Reaction catalyst; Cell recognition; Signal reception. Source: http://www.academyofone.org
Source: https://www.youtube.com/
Fluid mosaic model Phospholipid heads are hydrophilic and polar, whereas tails are hydrophobic and non-polar; Heads face the outside of the membrane, tails face the inside. Attraction between the phospholipids is very weak: They are constantly switching places; The membrane can rapidly reform if broken. Many factors affect the fluidity of the membrane: Temperature, cholesterols, double-bonded tails, tail length. Source: https://figures.boundless-cdn.com
Group Work Divide into five groups: Diffusion & Osmosis; Facilitated diffusion; Primary active transport; Secondary active transport; Endocytosis and exocytosis (membrane-assisted transport). Research the following information: Function (what it does); Mechanism (how it does it); Role (why it does it advantages and drawbacks); Potential illnesses / problems.
Cell transport Passive: Particles are moved by concentration gradients (differences in particle concentration); Some particles move easily through the membrane, while others rely on proteins. Active: Generally used to move particles against concentration gradients; Requires energy, usually in the form of ATP molecules.
Cell transport: Diffusion Particles in and around the cell are in constant random motion: Particles move from high to low concentration. However, the cell membrane generally prevents large, charged or polar molecules from passing. Source: https://qph.ec. quoracdn.net/ Source: https://s3-us-west-2.amazonaws.com/
Cell transport: Osmosis Water may diffuse through the membrane like other particles; The diffusion of water is called osmosis. Concentration of ALL solutes = osmotic concentration and determines direction of osmosis. Source: http://antranik.org
Cell transport: Facilitated diffusion Some particles need help passing through the cell membrane; Channel proteins: Create a hydrophilic tunnel to let particles through; Come in many shapes and sizes, but generally let ions and polar molecules pass (e.g. Na + ). Carrier proteins: Bind to molecules and change shape to help them pass; Usually transport larger molecules (e.g. Glucose). Source: https://s3.postimg.org
Cell transport: Primary active transport Moves particles against the concentration gradient; Requires ATP (energy); E.g. Sodium-Potassium pump: Source: https://s3.amazonaws.com
Cell transport: Secondary active transport Pumping ions across the membrane causes a gradient in concentration AND charge; This is known as an electrochemical gradient. Can be used as source for transport; E.g. Sodium-Glucose cotransport: Source: http://figures.boundless-cdn.com
Cell transport: Endocytosis & exocytosis Membrane-assisted transport occurs when the membrane folds and pinches itself to create a vesicle around particles; Used for larger macromolecules; Endocytosis: Membrane forms vesicle around incoming molecules. Exocytosis: Vesicles fuse with membrane to release molecules. Source: https://classconnection.s3.amazonaws.com
Cell transport: Summary Diffusion & Osmosis Particles follow concentration gradient through phospholipid bilayer Facilitated diffusion Particles follow concentration gradient through channel or carrier proteins Primary active transport Particles go against concentration gradient thanks to ATP Secondary active transport Particles go against concentration gradient thanks to electrochemical gradient Endocytosis & Exocytosis Membrane forms vesicles to transport particles